1. Field of the Invention
This invention relates to a cyanoacrylate adhesive containing a pyrylium salt as a fluorescent dye and to its use.
2. Discussion of Related Art
Adhesives of this type are already known. Thus, EP 0 105 062 B1 describes a cyanoacrylate adhesive containing at least one dye from the group consisting of C.I. Solvent Green 5, C.I. Acid Red 50 and C.I. Acid Red 52 in a quantity of 5 to 1000 ppm, based on the monomers. The disadvantage of these dyes lies in their bright, clearly visible color, particularly where the parts to be joined are transparent. In addition, the dyes are poorly soluble in the monomers. Accordingly, it is not possible to prepare a master batch of cyanoacrylates and the dye, i.e. a stock mixture of cyanoacrylates with a high concentration of dye which the user himself is then able to dilute to the extent required by the particular situation.
Against the background of this prior art, the problem addressed by the present invention was to provide a cyanoacrylate adhesive containing a fluorescent dye, the dye showing very little, if any, inherent coloration in visible light and lending itself to use in relatively large quantities without any adverse effect on the storage stability and adhesive properties of the adhesive.